1. Field of the Invention
The present invention relates to a time tracking technique for channel estimation of a mobile communication receiver. More particularly, the present invention relates to a time tracking method and apparatus in which a tap position of a channel estimator is shifted to a maximum peak power position when a delay profile of a received multipath signal is varied due to an obstacle or a high-speed movement of a receiver.
2. Description of the Related Art
As high-speed mobile communication systems such as High Speed Packet Access (HSPA) or Wideband Code Division Multiple Access (W-CDMA) of the 3rd Generation Partnership Project (3GPP) have been recently standardized and commercialized, equalizer-based receivers suitable for high-speed transmitted signals are being researched and developed in various forms.
Normally, such an equalizer-based receiver is composed of a channel estimator and an adaptive equalizer. A channel estimator has been proposed that has a long enough tap to obtain all delay profiles of signals received via a multipath. In addition, an algorithm for an adaptive equalizer is being developed to use estimated multi-tap channel values. For example, considering a delay profile of a multipath channel, a conventional receiver is designed to have a sufficiently long tap and also uses a technique to activate or inactivate taps of a channel estimator according to the state of the channel.
Another proposed channel estimator and equalizer employ a 2× chip rate self-tracking technique. This technique analyzes properties of a delay profile of a multipath receiving channel and, in order to perform a slew control, shifts tap positions of a channel estimator and equalizer by a half chip according to channel variations. This technique reduces performance loss which may often be incurred in an equalizer-based receiver using fixed taps when a delay profile of a received multipath signal is varied due to an obstacle or a high-speed movement of a receiver.
In a slew control method of the related art, tracking is performed by adjusting tap positions at intervals of only a half chip when energy distribution of a multipath fading channel is varied. More particularly, tracking of tap positions is always performed at intervals of a half chip even though the position of the maximum peak power disagrees with that of a pre-allocated multi-tap (i.e., a reference tap). However, this may deteriorate channel estimation capability due to great difficult in performing fast tracking.
Therefore, a need exists for an advanced slew control technique which allows a fast agreement between positions of maximum peak power and a pre-allocated multi-tap.